Influence Of Magnetic Field Configuration Research Articles

Influence of Magnetic Field Configuration in Helicon-Negative Ion Source on Increase of the Efficiency of NNBI Heating System

The influence of the magnetic field configuration on the performance of a helicon-based negative ion source is investigated with simulation experiments. Using COMSOL Multiphysics software, a three-dimensional simulation model for a negative ion source, based on a helicon plasma source, is presented in two magnetic field configurations: uniform and nonuniform configurations. The helicon plasma source employed a Nagoya-type antenna to apply radio-frequency (RF) power at a frequency of 13.56 MHz. The injected gas is hydrogen with a flow of 10 standard cubic centimeters per minute. Using a three-dimensional model, helicon wave propagation in the presence of a magnetic filter and the energy absorption mechanism in the helicon system are investigated. In this context, in the presence of the two magnetic field configurations, the influence of the important parameters’ working pressure and RF power on the optimization of negative ion production under volume mode is studied. Six electromagnetic coils at the same current are used for producing the magnetic field in both cases of uniform and nonuniform configurations. The variation of the electron density and electron temperature, in both regions of driver and expansion, are calculated and represented with respect to the different power and the gas pressure. The simulation results of the negative ion density in the expansion region for the uniform and nonuniform magnetic field configurations are compared. The results indicate that at the same applied current of coils, the negative ion density in the presence of the nonuniform magnetic field is about 1.75 times higher than the negative ion density of the uniform case. Moreover, the results show that the negative ion density is decreased by decreasing the magnetic field of the driver region in the nonuniform cases.

Influence of magnetic field configuration on plasma characteristics and thin film properties in dual magnetron reactive high power impulse magnetron sputtering discharge with Al in Ar/O2 mixture

In this work, the influences of the magnetic field configuration (mirror-field and closed-field) on plasma parameters and ion flux dynamics of dual magnetron reactive high power impulse magnetron sputtering (R-HiPIMS) with Al targets in Ar/O2 mixture were studied by time-resolved Langmuir probe and time-averaged mass spectrometer. Compared with mirror-field configuration, the electron density (ne) in the closed-field discharge is obviously higher while the plasma potential (Vp), floating potential (Vf) and effective electron temperature (Teff) were lower. Time-averaged mass spectrometer results showed that the plasma compositions in both configurations were similar. The ion energy distribution functions (IEDFs) recorded at both discharges consisted of three components: a main narrow peak at low energy followed by a broad shoulder and then a high energy tail. Compared with the closed-field discharge, the mirror-field discharge exhibited higher peak energies but lower ion fluxes. For both discharges, the ions intensity increased immediately after the start of the negative voltage pulse. The signal for the mirror-field discharge peaked exactly at the end of the pulse, whereas fluxes of the ion species in the closed-field configuration reached the highest value 10μs after the voltage pulse termination. To investigate how changes in the magnet arrangement affect the film properties, Al2O3 thin films were deposited and characterized. It is confirmed that the magnet configuration appeared to have little influence on the deposition rate. In addition, high average energy per deposited atom in the closed-field discharge resulted in a well densified and stoichiometric crystalline Al2O3 film.

Radio-frequency magnetized ring-shaped hollow cathode discharge plasma for low-pressure plasma processing

Influence of magnetic field configuration on ring-shaped hollow cathode discharge has been investigated in order to perform high-density plasma sources under a low gas pressure of a few tens mTorr. Three typed arrangements of permanent magnets such as (a) NS-NS, (b) NS-SN and (c) NS are examined. The NS-NS arrangement has a divergent profile with a peak in axial direction in hollow cathode. The NS-SN placement forms a cusp profile with a mirror configuration in axial direction. In final, the NS setup assigns a conventional divergent field. For the cases of (a) NS-NS and (b) NS-SN arrangements, their plasma density keeps a higher order of magnitude of 1011 cm−3 at the wide range of gas pressure of 10–200 mTorr. On the other hand, the NS arrangement maintains only the order of magnitude of 1011 cm−3 at the region of gas pressure more than 30 mTorr. All radial profiles of plasma density near the hollow cathode show non-uniformity like M-shaped distribution. However, it is found that the uniformity of their radial profiles depends on the arrangement of permanent magnets.

Microstructural modification of TiN deposited by magnetron ion plating: Influence of magnetic field configuration

Three operating modes of a single magnetron were used during deposition processes: balanced magnetron configuration with no external magnetic field and no bias potential applied (magnetron only), balanced magnetron configuration with permanent magnet cages positioned around the deposition volume to form a closed field configuration (BM mode) and an unbalanced magnetron closed field configuration (UBM mode). The influence of the deposition rate and ion j i to deposited metal atom j m flux ratio j i/ j m at the substrate surface on the texture evolution was discussed. The deposition rate distribution over the target to substrate distance was found to depend on magnetic field configuration and also to be different in metallic and reactive mode. In UBM mode it was possible to obtain nearly constant bias current density along the deposition volume at the constant bias potential. The preferred crystalline orientation was changed from (200) to (111) by increasing target to substrate distance in both BM and UBM modes, while the film deposited in magnetron-only configuration preserved (111) texture.

Influence of magnetic field configuration on the deposition conditions in an unbalanced magnetron system

Three configurations of a magnetron sputter ion plating system were considered: the double magnetron open field configuration, single magnetron multipole open field configuration and single magnetron multipole closed field configuration. The (Ti,Al)N coating was deposited in the double magnetron system onto substrates oscillating in and out of high ionization degree plasma obtained by overlapping two magnetron discharges. A strong influence of plasma “density” on the coating growth was found. The experiments were also performed in two single magnetron systems in order to find approximately the region in which a plasma suitable for coating deposition is generated. A rough estimation of high density plasma pattern was given based on voltage-current characteristics of the magnetron discharge. Both single magnetron systems were found suitable for hard coating deposition, but the higher bias current density at the substrate surface had been measured in closed field configuration under similar deposition conditions.

Influence of magnetic field structure on the conduction cooling of flare loops

A simple model facilitates calculation of the influence of magnetic field configuration on the conduction cooling rate of a hot post-flare coronal plasma. The magnetic field is taken to be that produced by a line dipole or point dipole at an arbitrary depth below the chromosphere. For the high temperatures (T ≳ 107 K) produced by flares, the plasma may remain static and isobaric. The influence of the field is such as to increase the heat flux (per unit area) into the chromosphere, but to decrease the total conduction cooling of the flare plasma. This leads to a significant enhancement of the total energy radiated by the flare plasma.